1. Field of the Invention
The present invention relates to controlling the deposition or buildup of foulants such as polynuclear aromatic compounds in processing equipment and, more particularly, to processing equipment used to process product streams produced by dehydrogenating aliphatic hydrocarbons.
2. Description of the Prior Art
There are numerous processes for dehydrogenating aliphatic hydrocarbons containing not less than 2 and not more than 5 carbon atoms per molecule. One such process, marketed by UOP as the "Oleflex," process involves dehydrogenating the aliphatic hydrocarbon using a catalyst containing at least one metal or metal compound selected from Group VIII of the Periodic Table.
In particular, the Oleflex process and other dehydrogenation processes are used extensively to dehydrogenate isobutane to produce isobutene, the latter being subjected to an etherification reaction to form methyl tertiary-butyl ether (MTBE), a key component of reformulated gasolines.
In a typical refinery operation to produce MTBE, isobutane is dehydrogenated to produce a dehydrogenated product stream (DPS) containing isobutane and isobutene. Prior to being etherified, the DPS containing the isobutene is passed through a processing train to process the gaseous dehydrogenation product stream to remove any unwanted liquids and other contaminants formed in the dehydrogenation reaction and to compress the gaseous stream.
It is known that in the dehydrogenation of aliphatic hydrocarbons such as isobutane, aromatic compounds are also formed, such aromatic compounds including polynuclear aromatics (PNA). Over and above the fact that the aromatics must be removed from the product stream from the dehydrogenation reaction so as to prevent any unwanted contamination of products produced using the DPS, it is known that certain of the aromatics, particularly the PNA such as anthracene, are prone to deposition on the internal surfaces of equipment in the processing train used to process the DPS. This deposition of the PNA results in fouling of piping, exchangers, valves, and other equipment in the processing train, forcing frequent and expensive shutdowns so that the equipment fouled with the PNA can be cleaned.